You can use lipid without a voltage regulator depending on the setup you run. Some receivers can run on higher voltages, but the key are your servos. Most servos are designed to run on or about 6 volts. Lipos have a much higher voltage over the discharge curve thus putting additional strain on servos not designed to run higher voltages.
I've bought the robitronics Lipos from lockmouth and he is very trustworthy. Couldn't be happier with thief performance.